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Posts posted by NowThatWeKnow

  1. The article said:

    "The level of activity was so great that at times it equalled the amount of the gas released at some of the most methane-rich locations on Earth."


    While microbial life on Mars is not out of the question, I doubt there is enough for this significant amount of methane detected.

  2. I'm not sure what the paradox is here. If you have two observers moving away from each other at 0.99c, both observers will see this to be the case. To see this it doesn't matter who did the accelerating. To increase the separation speed one would have to add energy, and to calculate this use the proper equation, which diverges at c.


    Using the wrong equation might give you an answer that exceeds c, but that's not a paradox.


    Houston control sends the mother ship from Earth on a trip to a near by star. After accelerating to a separation speed from Earth of .99c they are at rest in their inertial frame. Since inertia says it will "stay in motion in a straight line unless acted on by an outside force", little or no power will be needed to maintain the separation speed. At this point we have symmetry between the Earth and the mother ship it it makes no difference who accelerated away from who.


    Space man Joe decides it it taking too long and gets into a secondary space ship and blast off towards the destination star at a separation speed from the mother ship of .99c. This would cause a separation speed from Earth exceeding the speed of light. Can you explain where I am going wrong with out complicated equations?


    (and you thought you got rid of me :embarass: )

    Welcome Dark_anzel

  3. This is a long-standing issue of definitions. Using the normally-used definition of mass (the invariant mass or so-called rest mass) this isn't true. It holds if you use a certain definition called the relativistic mass, but that causes other difficulties.


    What is true with either definition is that the kinetic energy's dependence on mass diverges at c, and then we reach the conclusion of it requiring infinite energy to do so.


    So, two objects moving away from each other at .99c would see each other as rest mass plus the energy needed for relativistic speed for a total of relativistic mass. This is regardless of who accelerated away from who and they would see them selves as rest mass only. How do we tell who was the one that accelerated in the first place? The object that was at rest in the first place could accelerate away from the other object increasing the separation speed. The object that increased speed in the first place could not increase the separation speed without exceeding light speed. Another paradox that could be explained by an ether, or am I looking at it wrong?

  4. At 186,000 miles per second it takes 500 seconds for light to reach us from the sun. Due to time dilation from gravity, clocks on Earth, the Sun and in 0-G in space would run at different times. (1) Which clock would show 500 seconds? It seems that light would travel at a constant speed but only relative to its current location considering gravity. Also, (2) would an observer in space see the speed of the light beam change as gravity changed? To prove general relativity we observed light being bent around the Sun. (3) Is space actually warped from gravity or is time dilation from gravity causing the bend?

  5. The satellites experience a centripetal acceleration, because they are in a rotating frame. Even though the speed stays the same the velocity changes (direction of motion) so it's still an accelerating frame.


    3. The breaking of the symmetry does all happen during the acceleration. But it's also independent of the amount of acceleration (i.e. the turnaround can be instantaneous or slow, and that won't affect the basic answer — the amount of dilation depends on v and the length of the trip)


    I guess the stars in the Milky Way could be considered a rotating frame but on a scale that would have little impact on local motion.


    3. I understand what you are saying but it does seem to create a paradoxical situation. Distant galaxies in opposite directions are separating from each other at speeds greater than light so has time stopped or is it running backwards in the other galaxy if they could see each other. An expanding ether of space independent of local motion would make sense to me.


    You have answered some basic questions and I feel further reading will make much more sense to me. Thank you very much.

  6. In SR inertial frames have no acceleration, i.e. Newton's laws describe the motion of the object. Any objects moving with respect to each other are in different inertial frames. ..In general relativity one finds that an object falling freely in a gravitational field is also in an inertial frame...The earth and satellites are not in inertial frames, again owing to rotation. However, we "fake" an inertial frame...

    Excellent, excellent, excellent, I think. This is where the definition of inertial frames should start. Please bear with me, I think I see a light in the distance and it appears to be blue shifted.


    I am in a inertial frame when in my car at constant speed and can accelerate or decelerate to a different frame (relative to any other object at a fixed location or moving at a constant speed).


    The Earth is in a "fake" frame because of rotation but "the satellites are in orbit, and thus accelerating (centripetal acceleration)" and not a frame?

    Not sure I see why the satellite is considered accelerating though, unless it has to do with the Earth rotation.


    1. If a space ship takes a month to accelerate to .99c would it be wrong to look at it as a variable frame during acceleration? An entire trip could be made without a constant speed. How do we deal with time dilation while not at a constant speed?


    2. Twin "a" takes a trip in space and comes back young. Twin "b" doesn't like being older then "a" so "b" takes a trip and comes back the same age as "a". Right?


    3. I am still confused on what determines which twin will age faster unless it all happens during acceleration. During the time of constant speeds relative to each other, their clocks should be symmetrical, unless there is a space ether and not just a metric.


    A propeller is not in an inertial frame because it is accelerating, owing to the rotation.


    4. So at a constant rpm would the hub and tip experience time dilation because of the different speeds?



    5. Does the bolded text at the top contradict each other?

  7. Identical, ideal clocks in two inertial frames will run at different rates, and accrue time (phase) differences. This difference, however, will be symmetrical — each frame will observer the other one as running slow. An acceleration breaks this symmetry, and one must accelerate in order to bring the clocks into the same frame. The accelerated clock is the one that will end up running at the "wrong" rate.


    Maybe my confusion is because of my understanding of inertial frames. For kinematic dilation, do you have to be experiencing a G-force from acceleration to be in a different frame? Or using GR, be experiencing more or less then 1 G-force from matter to be in a different frame? If this is not the case please give me an example or two of different inertial frames. Would a high speed propeller hub be in a different frame then the tip while rpm increased?



    GPS clocks aren't in an inertial frame, even when adopting an earth-centered inertial frame of reference, where we assume an observer on the earth is at rest. The satellites are in orbit, and thus accelerating (centripetal acceleration). They actually run fast, because the gravitational dilation has a greater magnitude than the kinematic dilation, and they are in a smaller potential.


    So, "GPS clocks aren't in an inertial frame". Do you mean different then Earth's frame? Is time dilation symmetrical (only considering kinematic dilation) between the satellite and earth? I have a few more questions but I will be able to word them better if my questions so far are answered.


    Thank you for the reply. I did quite a bit of research before asking these questions but for some reason (especially SR time dilation) the clear picture eludes me.

  8. After reading several articles on time dilation and inertial frames I still have a question. The "Twin Paradox" at http://www.phys.unsw.edu.au/einsteinlight/jw/module4_twin_paradox.htm

    Made it sound like the acceleration and deceleration is what caused time dilation. That clocks in two inertial frames would stay synchronized as long as they were at rest in their frame, even if they were separating (without power) from each other.


    I must have missed something because "The Universe" Program pointed out that GPS satellites had to adjust their clocks because of their orbit speed using SR. Wouldn't the GPS unit on Earth and the satellites both be at rest in their own inertial frame? After acceleration is stopped it seems there would be no way for the clocks to know which one is fast and which one is slow. :confused:

  9. OKay, fine. GIVE ME A BREAK THOUGH, YOUR SINGLING ME OUT BECAUSE I RESPONDED TO A POST. Seriously, he asked how big space was, i gave him the answer i believe to be true. Im 15 for gods sake, i've not even set foot on a college yet, so just ignore me if u don't agree with me


    15? You are doing well for your age. I am happy to see young people interested in science.


    From your perspective it may seem like Martin is singling you out but I do not think that is the case. He is a moderator and is just enforcing the rules. If you re-read his first reply to you in this thread, he took a very gentle approach to calling you on speculation. I recently came from a forum that was not moderated so speculation and other things turned order to chaos. There is a place and time for speculation and there is a area for it in these forums. Questioning paradoxical theories and observations that seem to contradict physical laws lead to some speculation that seems to be allowed.


    Now, lets have some fun.

  10. In case it isn't clear, when people say you'll "slow down," it's more accurate to say that you'll accelerate to a closer reference frame to the average in the Milky Way. And you'll do this because of collisions with objects and gravitational influences, not because there is some inherent tendency to make objects move at the same velocity. There is not inherently a force needed to "maintain velocity," since every object is already at rest in its own reference frame. And it is meaningless to say that an object has a certain velocity without also specifying the reference frame in which it has that velocity.


    ...just so we're clear.


    Thank you, I can relate to what you say. One thing that is puzzling is the uniformity of the expansion of the universe since you say "...not because there is some inherent tendency to make objects move at the same velocity." I take that as saying things would be all over the place (without gravity) yet we observe Hubble's law at work. It is hard for me to ditch the view of a fabric of space to synchronize it all.

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    After looking up some statistics we can look at heavy element planets from a different angle. Just a thought and not a theory.


    There are at least 200 billion stars in the Milky Way and probably many more.


    The latest figures used in the drake equation says there could be heavy element planets around 60% of the stars, maybe more. That says 120,000,000,000 stars have planets


    The universe is a little over 13 billion years old but stars and supernovae were not present in the very beginning.


    We observe about 2 supernovae every 100 years in the Milky Way. That would be about 260,000,000 in 13 billion years.


    That would come up with one supernova for every 461 stars with heavy element planets.


    The question is would one supernova provide enough heavy elements to support that number of solar systems with planets? If not, it had to come from somewhere else.

  11. The individual photos were at no time stopped.

    I remember on the History channel "The Universe" light speed episode that light was stopped in some sort of sodium gas (I think sodium gas). Would that be considered "changing the effective refractive index"? They pretty much controlled the speed of the light and we watched it happen. They were real proud of themselves.

  12. I could be wrong but i believe i read somewhere that calculations of the expansion of the universe show that most of what we can see is still on our side of the cosmic horizon. For it to all be that far away by now, it would have to be traveling at a speed that is almost unimaginable, so I'm fairly certain that most of it is still with us. However, there could be parts of it that were never visible, if the big bang created more than just the visible universe.


    Let me start with a statement from a scientist on the History channel "The Universe" program. "There is no reason to believe that the universe isn't larger that what we observe" and "the only thing faster then light is the expansion of space itself."


    The light we see from the most distant galaxies has taken about 12 billion years to reach us. The red shift indicates it is moving away at close to the speed of light. However, the light we see today from that galaxy was sent when that galaxy was only 4.8137 billion light years away and today that galaxy is 23.587 billion light years away. The space expansion factor at that distance is 4.9. There may be galaxies past this point but space may be expanding faster then light travels so we can not see them or the light has not reached us yet. I suspect these most distant galaxies light will drop off the radar screen before long.


    So, we can see a galaxies light that is currently 23 billion light years away but the light leaving the galaxy now will never reach us. Working the calculations at different distances tells me that a moderate size (thick) ring of the most distant galaxies are putting out light today that we will never see. Does that answer your question and make sense to you?


    if anyone sees any errors in my #'s please chime in.

  13. There is no rest frame of space, any rest frame you select is as correct as any other (with the exception of a rest frame moving at c).


    Please bear with me as this is making my head hurt. I will try to ask a simple question that has a yes or no answer. I really am not trying to be a pain. Klaynos is not the only one with much more physics knowledge then me so any one that can answer in layman terms please chime in.


    Since the Milky Way stars are fairly constant in the short term I will use them as a reference point. Lets try to ignore gravity for this question.


    1. your said (the supernova matter thrown out) "It will slow because there is some friction in space." Are you saying relative to the stars in the Milky Way it will slow?


    2. I am traveling to a near by star in my space ship. I am almost half way there traveling at .99 relativistic speed with two light years to go. I shut down my propulsion system. Relative to my destination star, will my speed slow down?

  14. We have to make a distinction between:


    Technilogically impossible.

    Physically impossible.


    The first one means we just don't know how to do it, the second one means it is against a fundamental physical law.


    Wikipedia says:

    "Laws of science may, however, be disproved if new facts or evidence contradicts them."

    We have to remember that the smartest men on the planet two hundred years ago would shake there heads in total disbelief seeing the impossible things (in their mind) that we are doing today.

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    IMO it is this ability to locate information and put it into a usable form that ties human knowledge together for all of us and enables faster advancement, actual understanding is less important than ability to understand.


  15. It will slow because there is some friction in space. And the gravity from the galaxy will move it into an orbit I'd imagine...


    But it is of course at rest in it's own rest frame...



    Is this right?

    The object at rest in it's own frame is not at rest in the larger frame of the space and stars around it. As the objects frame travels through the larger frame it will slow and eventually come to rest so both will be in the same frame again.


    This sounds like space is more then just a metric and you have to actually travel through it.

  16. This kick can be substantial, propelling an object of more than a solar mass at a velocity of 500 km/s or greater.


    That brings up a question I have had for awhile. So, while we have all these great minds together:

    Will this speed (in relationship to it's starting point) be maintained? Or will it eventually come to rest in it's current location. It seems the frame it is in would require sustained power to maintain speed from an observers prospective. So would E=MC^2 eventually bring it to rest in its current location? Or would after reaching relativistic speed in your space ship, would you have to maintain power to maintain speed (relative to your starting point)?


    Edit - This does pertain to the OP since it could explain the distribution of heavy elements.

  17. Where else do you think we might get heavy elements from?


    Wikipedia says:

    "Supernovae play a significant role in enriching the interstellar medium with higher mass elements".


    What do you think they mean by significant? It sounds like they are leaving themselves open for other sources of heavy elements.




    "The buildup of heavy elements from lighter ones by nuclear fusion. Helium and some lithium was produced by cosmic nucleosynthesis just after the Big Bang, but today most element-building nucleosynthesis takes place in stars."


    What do they mean by "most"? Maybe we do need nuclear fusion but do we need a supernova? What is happening in those big black holes and what is shooting out of them? Nuclear fusion and heavy elements?


    I do not have the answers but "NowThatWeKnow" usually has consequences. In 10 years from now it will be :doh:

  18. Not our star, but our planet. The heavy elements, especially those heavier than iron, are quite rare in stars...So, supernovas are the only source I know of for the heavy elements.


    Thank you for your reply. Wikipedia says:

    While "supernovae play a significant role in enriching the interstellar medium with higher mass elements", I suspect it ia a collective effort and not a single supernova per heavy element solar system scenario. It seems we are on are way to discovering that most stars have planets and heavy element solar systems will be common. I think that assuming supernovae are the only source for heavy elements is unwise, sort of like NowThatWeKnow.


    I did some reading and learned something because of this thread. Next I will try to learn to read then post rather the post then read. :)

  19. so i pose this question...

    how would an alien speak english???(other than watching us for millenia and learning our language)


    That is good. You can ask and answer your own question in one sentence. ;)

  20. Do you not agree that quality of information is far superior to quantity? And if the information of higher quality causes it to reach more people, then an increase in communication has also occurred. Voila :)


    You bet! That is why I added ("A lot of knowledge is garbage but it goes with the territory.") to my last post. I am personally astonished that we have gone as far as we have with all the double digit IQ neanderthals in the world. :eek:

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    Sure, but in an information super highway, much knowledge is buried under a ton of garbage few want to sift through, for more will have piled up in the meantime.


    Yet we have walked on the moon and have a robot on Mars. Isn't it amazing?

  21. This is not entirely accurate.

    If you must attend a lifetime of school to understand the information, how can it be knowledge until you intimately grasp it?


    Think of it as a collective entity. You personally do not have to understand something for it to be knowledge. As long as someone understands it. A lot of knowledge is garbage but it goes with the territory. There are 6.7 billion people on the planet to come up with new stuff and that # goes up by 200,000 per day. Good for knowledge but bad for planet Earth in the near future. Have you seen the world clock? Check out how many chickens the world consumes in one day. http://www.poodwaddle.com/clocks2.htm

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